1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and devices and, more particularly, to mechanisms and techniques for using a ram blowout preventer (BOP) when a pressure is applied from above or below the BOP.
2. Discussion of the Background
One apparatus for sealing a well is the ram BOP. The ram BOP (herein simply BOP) is a safety mechanism that is used at a wellhead of an oil or gas well. The BOP may be used for offshore drilling and also for land-based drilling. The BOP is configured to shut the flow from the well when certain events occur. One such event may be the uncontrolled flow of gas, oil or other well fluids from an underground formation into the well. Such event is sometimes referred to as a “kick” or a “blowout” and may occur when formation pressure exceeds the pressure generated by the column of drilling fluid. This event is unforeseeable and if no measures are taken to prevent and/or control it, the well and/or the associated equipment may be damaged.
The BOP may be installed on top of the well to seal the well in case that one of the above events is threatening the integrity of the well. The BOP is conventionally implemented as a valve to prevent the release of pressure either in the annular space between the casing and the drill pipe or in the open hole (i.e., hole with no drill pipe) during drilling or completion operations. However, during various tests of the rig, a pressure from above the BOP needs to be applied and this pressure needs to be confined to a space above the BOP.
FIG. 1 shows a well 10. A wellhead 12 of the well 10 may be fixed to the seabed 14. The BOP 16 is secured to the wellhead 12. FIG. 1 shows, for clarity, the BOP 16 detached from the wellhead 12. However, the BOP 16 is attached to the wellhead 12 or other part of the well. A drill pipe 18 is shown traversing the BOP 16 and entering the well 10. The BOP 16 may have two ram blocks 20 attached to corresponding pistons 22. The pistons 22 move integrally with the ram blocks 20 along directions A and B to close the well 10.
A cut view of the BOP 16 that shows the ram blocks 20 is shown in FIG. 2. The ram blocks 20 are shown closed inside a cavity 24. The cavity 24 may be bordered, at one end, by a top seat 26 and a wear plate 28. The part of cavity 24 bordered by the top seat 26 and the wear plate 28 may contact the ram blocks 20 tighter than the remainder of the cavity 24. For this reason, the top seat 26 and the wear plate 28 are fixed to the body of the BOP 16 by screws. The ram blocks 20 may include a packer 30 (which may be an elastomer) and a top seal 31, which seals the well 10 when the ram blocks 20 are closed.
When the ram blocks 20 are closed and a large pressure exists underneath, the ram blocks 20 are pushed upwards so that the ram blocks 20 slightly move towards the top seat 26. Thus, an elastomer 31 that exists between the top seat 26 and the ram blocks 20 is squeezed, achieving the sealing of the well. However, it is noted that the same is not true for a conventional BOP when the high pressure is applied on the ram blocks 20 from above, as the elastomer does not extend between the ram blocks 20 and the wear plate 28 but only between the ram blocks 20 and the top seat 26.
FIG. 3 shows a detailed view of the top seat 26. A screw 32 is shown entering the top seat 26 from right to left up to a lock ring 34. The lock ring 34 is disposed around the top seat 26. The lock ring 34 is housed partially in a groove 36 of the body of the BOP 16 and partially in a groove 38 of the top seat 26. This arrangement prevents the top seat 26 to fall into the cavity of the BOP 16. FIG. 3 also shows that a seal 40 is disposed in another groove 42 of the top seat 26 for preventing a pressure from the well entering the cavity of the BOP 16.
The conventional ram blocks 20 are designed to seal off the well in collaboration with the top seat 26 only when a pressure is applied from below the ram block, i.e., a pressure presses upwards the ram block 20 so that packer 30 and top seal 31 become active and effectively seal off the well.
However, occasionally the operator of the well needs to conduct wellbore pressure test, i.e., apply a pressure from above the BOP. With a conventional ram BOP as illustrated in FIG. 2 it is not possible to run this test as the ram BOP will not seal the well because the ram blocks will not press the top seat 26. Thus, one possibility is to provide another device (a reverse BOP) next to the BOP such that the test mode can be performed. This approach increases the footprint of the equipment and the cost of the rig, which is undesirable.
Accordingly, it would be desirable to provide systems and methods that achieve the sealing of the well when pressure is applied both from above and from below and to avoid the above noted shortcomings.